Surface sizing with sizing agents and glycol ethers

ABSTRACT

In this invention a composition is applied to the surface of paper comprising a glycol ether based polymer that provides enhanced ink-jet print quality. The advantage of using the composition is that it improves ink-jet printing on the paper without significant loss of water hold-out. More specifically, the paper is uncoated and has been treated on the surface with the following materials and dried to the point of usefulness. These materials are:
     1) one or more compounds that increase water hold-out. These are known as sizing agents,   2) starch,   3) A glycol ether based polymer.

FIELD OF THE INVENTION

This invention describes the improvement of uncoated fine paper bytreatment of the surface of the paper with polymers based on glycolethers used in combination with starch and paper sizing agents. Theinvention results in paper with enhanced ink-jet print quality. Theenhanced qualities include less mottle on the printed images, lessstrike-through to the back side of the paper when printed, and enhancedoptical density of printed images.

BACKGROUND OF THE INVENTION

Glycol ether based polymers including those end capped with epoxy groupshave been added to paper for many years. As far back as at least 1972,U.S. Pat. No. 3,873,354A (1972) describes the addition of humectantsalong with salts, such as sodium chloride and calcium chloride, to paperto be used for electroreprographic (or electrostatic) printing, that iscopy paper. The humectants named included “polyethylene glycols andpolymers . . . ”. The humectant must be water soluble or water miscible.The size press is mentioned as a means of application and “anotheradditive which will typically be added to the size press solution is aconventional binder such as a starch, gum, casein, polyvinyl alcohol oracetate, animal glue, etc.”. The goal was to reduce the static build-upon the paper. The level of addition of salts was recited but not thelevel of humectant. However, in an example, about 0.05% of the paperweight of polyethylene glycol was added. This is greater than the leveluse by applicant herein. In addition the use of adducts of polyethyleneglycol are not mentioned nor is the use of polypropylene glycol oradducts of polypropylene glycol mentioned. The latter two are not watersoluble. There is no mention of the use of sizing agents in the paper.

U.S. Pat. No. 4,210,412 describes the use of “polyhydric alcohol” incellulose based textiles. The additive is used to swell the cellulose soit will accept dyes during a transfer printing operation. What is calledpolyhydric alcohol includes “polyalkylene glycols such as polyethyleneglycol of average molecular weight of 200 to 4000, polypropylene glycolof average molecular weight of 400 to 5000, polyethyleneglycol/polypropylene glycol block copolymers of average molecular weightof 400 to 5000 . . . mono- and diethers . . . and diesters . . . ” Theaddition levels were not given; but, the addition levels used in theexamples were higher than the current invention. For example, the levelused in Example 2 had polyethylene glycol added at 7.5% of thesubstrate. This is far greater than used in the current invention

US Patent application 20050104947 A1 describes treatments for paper toreduce the amount of cockle and curl and also to provide an ink-jetimage recording method. The treated paper is defined by its level ofwater absorption and a ratio of wet to dry tensile strength. The cockleand curl tendencies are lowered by decreasing the hydrogen bonds betweenfibers in the paper. The desired paper is obtained by two methods. Onemethod deals with the treatment of the pulp fibers before the sheet isformed such that the treatment compounds are located between fibers.Among the compounds that can be used are polyethylene glycolpolypropylene glycol block copolymers, polyoxyethylene fatty acidesters, and other nonionic surfactant type materials. Also materialssuch as monoglycidyl ethers can be used. A second method is to add tothe paper a heat-curable material or a thermoplastic material. Again thematerial must be located between fibers and in this case adhere fiberstogether. Epoxy resins are given as one class of suitable additives.Thus, there is no surface treatment of a paper sheet. The applicationexpands on what can be done by saying that the sheet can be treated bysurface sizing to apply a nonionic surfactant. Furthermore, thetreatment is also said to preferably include polyvalent metal salts suchas calcium chloride or a cationic polymer such as cationic starch.Either material can be added at levels that provide 0.1 to 2 g/m² ofmaterial to the sheet. The sheet weights of interest are 60 to 128 g/m².Therefore, the range of percentage addition is from 0.08 to 3.3%.

The addition of polyethylene glycol and polypropylene glycol to the wetend of a paper machine is described in U.S. Pat. No. 5,240,562 (issuedin 1993 to Procter and Gamble). The patent points out that polyhyroxycompounds like polyethylene glycols and polypropylene glycols havingweight average molecular weights from about 200 to 4000 can be used withquatemary ammonium compounds to give tissue paper a good combination ofsoftness and absorbency. This patent only covers the wet-end addition ofthe polyhydroxy compounds before the paper is dried. There is no mentionof the impact on ink-jet printing. The quatemary ammonium compound andthe polyhydroxy compound were premixed.

There are numerous patents concerning coated paper where a reactivepolymer hardener is added to the ink absorptive layer. A wide variety ofmaterials to crosslink the absorptive layer are known and they includediglycidyl ethers of glycol ether based polymers, such as polyethyleneglycol digylcidyl ether (PEGDGE). In US Patent 20050202188A1 PEGDGE isused in a ink-jet absorptive coating layer to crosslink polyvinylalcohol.

However, coated papers are very different from the paper of the currentinvention. A coated paper has one or more relatively thick layers oftreatment on one or both sides of a preformed paper. Such papers finduse in high-end printing application including high-end ink-jet printingapplications such as photographic paper. For ink-jet applications,coated grades have an absorbent layer composed of either a polymer thatabsorbs a high volume of liquid ink or a high level of filler that canadsorb a high volume of liquid ink. There are two uses of glycol etherbased polymers used in such coatings. First they may be added as anabsorbent material and secondly, diglycidyl ethers of glycol basedpolymers may be added to improve surface strength. European Patent0634284 discusses both such uses. The instant invention does not covercoated papers.

There are also other uses for polyglycol ethers in paper coatings. U.S.Pat. No. 5,746,814 describes the addition of the following compounds asdesizing agents in a more complex composition for coating of paper:poly(alkylene glycol); poly(propylene oxide)-poly(ethylene oxide)copolymers; fatty ester modified compounds of glycerol and poly(ethyleneglycol); and poly(oxyalkyene)modified compounds of sorbitan esters,fatty amines, alkanol amides, castor oil, fatty acid, fatty alcohol. Theoverall composition contains solvent, binder, desizing agent, anticurlagent, defoamer, biocide, antistatic agent, lighffastness promotingagent, and a filler. All of the coating applications fall into adifferent class of paper from the current invention and the coatingcompositions are significantly different as noted above.

US application, 20050013949 A1 concerns a coated paper. However, itsdescription of the base paper on which an ink absorbing layer would beapplied is described as. “Base paper employed for the paper support ofthe present invention is made employing wood pulp as a main raw material. . . It is possible to incorporate into base paper sizing agents suchas . . . strengthening agents such as starch . . . moisture retentionagents such as polyethylene glycol, dispersing agents and softeningagents . . . ”

U.S. Pat. No. 6,203,899B1 describes a printing medium comprising aliquid absorbent base material, an ink-receiving layer provided on thebase material, which comprises a pigment, a binder and a cationicsubstance, and a surface layer provided on the ink receiving layer. Hereagain the concern is a coated paper. It is described as fibrous pulp anda filler impregnated with a crosslinking substance. The crosslinkingsubstance is crosslinked to form nonswelling paper. The crosslinkingsubstance can be an epoxy. PPGDGE is specifically described. Along withthe crosslinking substance can be a polymer having a reactive group.Starch is one example of the polymer. The amount of starch is in therange that can be applied by a size press. The ratio of crosslinkingsubstance, starch, to crosslinking agent, PPGDGE, is from 100:1 to 1:1by weight. The range is different from the current invention where ourratio under preferred conditions is about 400 to 1 or less. A polyvalentmetal salt is mentioned as an option for crosslinking certain materials.The divalent metal ions that are optional additives of the invention ofthis disclosure do not crosslink starch.

U.S. Pat. No. 6,706,320B2 describes modifying a surface containing apolymeric material. In one claim, it is said the substrate can becellulosic and in another claim it is said the modifying agent can be acrosslinker. The crosslinker can be an epoxy compound such as diglycidylethers of polyols. However, the process of the patent requires thepresence of a polyamine as a surface modifying agent and that thepolyamine vaporize in the process. The epoxy compound reacts with theamine.

U.S. Pat. No. 5,746,814A includes polyethyleneglycol diglycidyl ether asone of the compounds that can be added to prevent paper from curling. Anelaborate composition for treating paper is described with a wide rangeof levels of each component. There are nine components in thecomposition and they can include water, starch as a binder, and PEGDGEas an anticurl or a desizing agent. Taking the maximum of starch in thecomposition and the minimum of PEGDGE one gets a ratio of 150:1. This isdifferent from that of the current invention. Furthermore the currentinvention does not require many of the other components listed such asantistatic agent or desizing agent or lightfastness promoting agent. Thecomposition is for treating paper that has already been imaged.

Hercules Incorporated has a patent (U.S. Pat. No. 6,207,258 B1) on theuse of divalent metal salts with sizing agents. It also had a patent(U.S. Pat. No. 6,051,107A) on mixtures of reactive and nonreactivesizing agents as pre-mixes and in paper treatment compositions. Thelater patent was not maintained.

SUMMARY OF THE INVENTION

In general one embodiment of the invention involves a paper compositionhaving applied to its surface a composition comprising a glycol etherbased polymer that provides enhanced ink-jet print quality. Theadvantage of the paper composition is improved ink-jet printing withoutsignificant loss of water hold-out.

More specifically, this first embodiment of the invention is an uncoatedpaper (based on wood pulp or other cellulose product based) that hasbeen treated on the surface with at least the following materials anddried to the point of usefulness. These materials are:

1) one or more compounds that increase water hold-out. These are knownas sizing agents,

2) starch,

3) a glycol ether based polymer.

The sizing agent will be present in an amount of 0.01% to 0.3% based ondry weight of paper.

The starch will be present in an amount of 1 to 8% based on dry weightof paper.

The glycol ether based polymer will be present in an amount of less than0.025% based on dry weight of paper.

One preferred composition is paper surface-treated with starch, sizingmaterial, a glycol ether based polymer and a divalent metal salt. Thesizing materials and glycol ether based polymers are defined below alongwith the addition levels.

The paper of the invention has improved ink-jet print qualities of lessmottle of printed areas, less strike-through of ink, and possiblyincreased optical density over paper not treated with all the componentsof the invention.

The sizing agents, as defined below, provide water hold-out. They mayalso improve the sharpness and optical density of ink-jet printedimages. The addition of sizing agents to paper is common. Likewisestarch is a standard additive to paper and thus, the invention in oneembodiment is the addition of sizing agent and starch with glycol etherbased polymers, such as polypropylene glycol diglycidyl ether. Anotheroption is that the paper as described above also contains a divalentmetal salt as described in Hercules patent U.S. Pat. No. 6,207,258 B1,incorporated by reference.

Any uncoated paper can be used, but a preferred paper is uncoated “fine”paper for printing and writing applications. Such paper typicallycontains bleached wood pulp, precipitated calcium carbonate, and starchalong with other materials deemed beneficial for preparing the paper orenhancing paper properties or reducing the cost of the paper. A typicaluncoated fine paper has a basis weight of 70 to 80 grams per squaremeter.

For the present invention, the three or four components of theinvention, listed above, may be added either separately or together tothe surface of the paper. Fine paper for printing and writing is usuallytreated before it leaves the paper machine on which it was made.

A clear distinction should be made between surface treatments andcoatings. Both are applied to paper that is already formed. Both can beused to enhance printing properties. A treatment is meant to modify thesurface of the paper but the general structure remains mostly unchanged.A coating creates a new surface. More material is applied with a coatingthan a treatment. Coatings are usually made up of a large percentage ofinorganic filler or pigment such as silica or clay or calcium carbonate.A coating covers the entire surface of the paper substrate blocking theporous nature of the paper and leveling the surface. With a “treatment”,the composition of the base sheet still has a large influence on finalproperties. For example, more wet-end sizing leads to a higher surfacetension in the final paper versus a low level of sizing. With a“coating”, the internal chemistry may affect the application of thecoating but does not have a direct effect on the final properties of thepaper. For example, internal sizing is covered up by a coating and willnot directly change the surface tension of the final coating unless itmigrates through the coating.

The method of applying the materials used in this invention is notcrucial as long as the application method for the materials iscontrollable and leads to the desired results. The most preferred methodof addition is for the starch to be dissolved in water by cooking andfor the other components to be added to the starch solution and then forthe resulting composition (the treatment composition) to be applied tothe paper with a paper machine size press.

A second embodiment of the invention is the composition used to treatthe paper. It is defined as a starch based solution containing at leastone paper sizing agent and at least one glycol ether based polymer andoptionally a soluble divalent metal salt such as calcium chloride andoptionally other additives common to the treatment of paper. Thetreatment composition allows for all of the additives to be appliedsimultaneously to the paper. This is an aqueous composition thatcontains:

sizing agent in an amount of 0.03-1%,

starch present in an amount of 1.5-12%,

glycol present in an amount of less than 0.25%.

The treatment composition consists predominantly of water in which abinder is dissolved. The binder is the predominant component aside fromthe water. The binder for this invention is predominantly starch. Otherbinders such a polyvinyl alcohol can be used in combination with thestarch. With the binder, other additives are typically added such assizing agents that hold out water and improve printing properties;optical brightening agents; dyes; and antistatic agents. Sometimesmaterials such as inorganic fillers are added. When fillers are addedthey do not constitute more than about 40% of the composition on a dryweight percent basis of the non-water components.

These compositions can also contain other common additives such assodium chloride and defoamer. The advantage offered by the secondembodiment of the invention (the treatment composition) is thesimultaneous treatment of the paper with a composition that leads to theimprovements listed above in the first embodiment of the invention. Thecomposition must be such that it is uniform and it can be applied to thepaper in a uniform manner.

Preferably, the glycol ether based polymers will be added to thetreatment composition so that they are applied to the paper with thepaper machine at the same time as the starch and sizing agent.

A third aspect of the current invention is a pre-mixture of the sizingagents and glycol ether based polymers and optionally a divalent metalsalt. The pre-mixture is then added to the starch based solution justdescribed. The pre-mixtures may be water based solutions or emulsions ordispersions. The glycol ether polymer will be 3-50% based on the amountof sizing agent.

A third embodiment of the invention comprises pre-mixtures of some ofthe additives that go into the surface treatment composition thusoffering the convenience of adding several materials simultaneously tothe mixture used to treat the paper. The pre-mixtures that are ofinterest for this disclosure will contain the following materials:

-   -   A water-based composition (i.e. a solution, latex, and or        dispersion) of one or more paper sizing agents, and one or more        glycol ether based polymers.

DETAILED DESCRIPTION OF THE INVENTION

The glycol ether based polymers used in this invention include polymerswith repeat units of ethylene glycol or propylene glycol or combinationsof them. There may be other functional groups along the backboneprovided they do not account for more than approximately ten percent byweight of the final polymer structure. There may be branching along thebackbone. The polymers can be end-capped with hydroxyl groups, ethers,gylcidyl ethers, esters, carboxylic acid groups, and other functionalityso long as the end groups do not account for more than 25% of the weightof the average polymer molecule.

The polymer compositions may have one, two, or more types of functionalend groups other than hydroxyl groups. There may also be one of moretypes of functional groups within the polymer backbone or grafted on toit.

Use of glycol ether based surfactants that fit the above criteria arepart of this invention provided they meet the remaining conditions givenbelow. Glycidyl ether end-capped polymers such as polyethyleneglycoldigycidyl ether and polypropyleneglycol digycidyl ether are useful also.

The average molecular weight of the glycol ether based polymers of thisinvention shall be from approximately 350 g/mole to approximately200,000. The polymer must be soluble or readily dispersible in water.The preferable average molecular weight is between 380 and 20,000 andmost preferably between 500 and 2000 g/mole.

The addition level of the glycol ether based polymers of the inventionis defined by the impact on sizing as defined in this invention and byconcentration. The glycol ether based polymers of the invention shouldnot cause greater than a 25% reduction in the level of sizing whenutilized under at least some portion of the conditions of thisinvention. For example, polypropylene glycol (PPG) may be used at a lowlevel but at a high level it interferes with sizing. The level ofaddition of the glycol ether polymers to the aqueous composition forsurface treating the paper shall be less than 0.25%. The level ofaddition in a premix with sizing agent should be less than 50% of theactive sizing agent by weight.

The paper substrate which is treated in the current invention cancontain wood based pulp from ground wood to chemically bleached wood ora non-wood based pulp or a combination of pulps. The paper can alsocontain usual paper making inorganic fillers such as calcium carbonateor clay and may also contain organic fillers. The paper can also containstrength additives, retention additives, internal sizing agents andother common paper additives such as alum. The preferred grade of papercan be any type suitable for ink-jet printing which can include finepaper to white-top liner board. The basis weight of the paper can beanywhere from 40 g/m² to 350 g/m². The preferred paper is any type ofprinting and writing paper including roll fed to sheet fed papers. Themost preferred is uncoated fine paper with a basis weight between 60 and100 g/m².

The starches that are suitable as part of the paper treatment can be ofany kind provided they can be dissolved in water and applied to thepaper. The starches can be from a variety of sources including corn,potato, rice, cassava root, and others used in paper making. Unmodifiedand modified starches can be used. Modified starches include oxidized,ethylated, cationic, anionic, amphoteric, hydrophobically modified, andothers used in paper making. The preferred starches have reducedviscosities such that solutions of greater than 6% solids can be used ona paper machine size press. The most preferred are those with reducedviscosity that are also are oxidized, ethylated, cationic, oramphoteric. The range of starch treatment based on the dry weight of thefinal paper is 1% to 8.0%. More preferably from 2% to 7% and mostpreferably from 3% to 6%. The range of starch concentration in thetreatment composition can be from 1.5% to 12% provided the viscosityallows for application to the paper substrate. More preferably theconcentration will be between 3% and 11% and most preferably between 5%and 10%.

The surface treatment sizing agents suitable for the current inventioninclude those that are termed reactive such as alkyl ketene dimers,alkenyl ketene dimers, and alkyl succinic anhydrides. Sizing agentstermed unreactive are also suitable and may be mixed or used with thereactive sizing agents as described in a previous Hercules' patent (U.S.Pat. No. 6,051,107A). Unreactive sizing agents may be used on their own.Unreactive sizing agents include soluble polymers such as styrene-maleicanhydride based polymers, styrene-esterified maleic anhydride basedpolymers, styrene acrylic acid and styrene methacrylic acid basedpolymers and insoluble polymers such as polymer latexes commonly used inpaper making such as poly(styrene/acrylic) resins, acrylonitrile/acylicresins and urethane polymers and insoluble polymer dispersions such asof ethylene/acrylic acid polymers.

The level of surface treatment sizing agent in the final dry paper willrange from 0.01% to 0.3% on a dry weight basis. Preferably the level is0.02 to 0.2% and most preferably it is 0.03 to 0.1%.

All of the above levels are based on both sides of a base paper beingtreated. However, the invention is applicable to treatment of one orboth sides. When only one side is being treated all of the above levelsrelating to the paper will be one half of the values listed.

The final paper may contain other additives that were included in theformation of the paper or were applied along with the surface treatmentor separately from the surface treatment. The additives applicable arethose which are usually utilized in paper. They include but are notlimited to the following: inorganic and organic fillers such as calciumcarbonate or hollow sphere pigments; optical brightening agents whichare also known as fluorescent whitening aids, pigments; dyes, strengthadditives such as polyamidoamines, promoter resins such aspolydimethyldiallylammonium chloride; adhesion promoting polymers suchas styrene acrylic latexes and styrene maleic anhydride based polymers;and inorganic salts such as sodium chloride and calcium chloride. Whenthe final paper contains a divalent metal salt it should be less than0.25% of the paper weight.

The methods of applying the paper treatment composition of the currentinvention are not limited provided uniform controlled application isobtained. The treatment may be made to paper formed on a paper machineand then only partially dried or it can be made on a paper machine todried paper or the treatment can be done separate from the paper machineto paper that was formed, dried, and moved. The preferred process is forpaper to be formed with a paper machine, partially dried, and treatedusing a paper machine size press, and then for the paper to be driedagain. The paper may be further modified by calendering.

The treatment composition, the second embodiment of the inventiondescribed above, has the same components just described. The starchsolution in water must be of dissolved starch and the viscosity must besuch that the solution, containing other components, can be applied tothe paper. The viscosity and not the solids of the starch solution isthe most critical factor; however, some starch materials can only bedissolved at very low concentrations before they become too thick touse. A paper maker will select a starch based on the properties itimparts to the paper as well as its ease of use and the ability to applythe desired level with the equipment being used. A preferred level ofstarch in the treatment composition is 3 to 12% and a most preferredlevel is 5 to 10%. Other materials such as polyvinyl alcohol may be usedwith the starch, if desired. The additional binder level will be lessthan the starch level.

Suitable sizing agents are described above. They are added to the starchsolution. The level of sizing agent in the composition will depend ontwo factors: the level of the starch composition applied to the paperand the desired level of sizing treatment. Typically the level of starchaddition is selected along with the starch solution concentration andthen the level of sizing agent in the starch solution is adjusted to getthe desired level of treatment. The level of sizing agent in the starchcomposition will be between 0.03 and 1% of the paper treatmentcomposition based on the active component of the sizing agent.

The level of glycol ether based polymer in the treatment compositionwill be determined in the same manner as described for the sizing agentlevel. The level of glycol ether based polymer will be determined by theamount of starch solution applied and the desired level of the polymerto be applied. The level of glycol ether polymer in the paper treatmentcomposition will be less than 0.25%.

The treatment composition may contain other materials as noted above forthe paper. When the treatment composition contains a soluble divalentmetal salt such as calcium chloride and magnesium chloride the level ofthe salt will be less than 20% of the starch level.

The sizing agents of interest were described above. One or more sizingagents can be combined. The form of the sizing agent will be as asolution emulsion or dispersion in water with suitable additives used toobtain desired stability. One or more glycol ether based polymers can becombined with the sizing agents. The sizing agent formulation may alsocontain a water soluble divalent metal salt such as calcium chloride ormagnesium chloride.

The amount of glycol ether based polymer versus sizing agents can befrom 3% to 50% polymer to active sizing agent. More preferably the levelof glycol ether based polymer to active sizing agent will be from 4% to35%. When added the level of divalent metal salt will be less than twotimes the total level of sizing agents.

DEFINITIONS

Sizing

Paper sizing refers to the ability of a paper to hold out a liquid orfrom preventing it from penetrating into or through the paper. Generallythe liquid held out is water. Sizing values are specific to the testused. Compounds that are designed to increased the hold-out of liquidsare known as sizing agents. Sometimes a specific type of sizing isreferred to such as an oil sizing agent. For the current work, thesizing and sizing agents are defined in terms of the ability to hold outthe water based ink solution used in the Hercules Sizing Test. The testis defined below. For a discussion on sizing, see Principles of Wet EndChemistry by William E. Scott, Tappi Press 1996, Atlanta, ISBN0-89852-286-2

Optical Density

Optical density is a measure of the inverse of the amount of reflectedlight off a surface. Generally and for the purpose of this invention, itis a measure of light reflecting off of a black printed area on a sheetof paper. Optical Density (OD) equals −log₁₀(reflectance). The testmethod utilized was to use commercial hand-held densitometer. It isfurther described below. The concept of optical density is explained indetail in an article by Allen Rushing found on the internet atwww.loglight.com/concepts&tools.htm.

Mottle

Mottle, or more accurately print mottle, refers to the unevenness of aprinted area. It can be blotchiness or variations in optical density.They are visible to the eye. The method used to measure the mottle willdetermine what value it has. The test method used is provided below. Anexample of print mottle is shown in FIG. 19.17 of Printing Fundamentalsed. Alex Glassman, Tappi 1985, Atlanta, ISBN 0-89852-045-2.

Strikethrough

Strike-through refers to the uneven penetration of ink through to theback side of a printed paper. It is not show through which is theability to see the printed image from the back side of the sheet butrather is penetration of the ink through or almost through the sheet.The ink penetration is often uneven and the strike-through will have aspeckled appearance on the back side of a large printed area. The methodused to measure the mottle will determine what value it has. The testmethod used in the current invention is provided below.

TEST METHODS

Preparation of Samples

Paper samples for the examples below were prepared by either alaboratory method or with a pilot paper machine. The general proceduresare described here. Specific details are listed with each example.

For the laboratory test, base papers were prepared ahead of time atWestern Michigan University on their pilot paper machine. The paperswere made without any size press treatment, that is no starch, sizingagent, or other additive was applied to the surface of the formed paper.The pulp used to make the papers was a 75%/25% by weight mixture ofhardwood and softwood bleached craft pulp as is typical of what would beused to produce commercial copy paper. The papers also containedprecipitated calcium carbonate, cationic starch, aluminum sulfate and aretention aid. Once made and dried the papers were cut into sheets andstored. The paper was later treated at the Hercules Research Center witha laboratory bench top puddle size press. The size press consisted of ahorizontal set of ten inch pinched rollers, one rubber coated and onemetal, through which the paper was fed. A puddle of the size presstreatment was held by the rollers and dams on the top side of therollers. The rollers were held together with 14 pounds of air pressure.The paper passed through the puddle as it was pulled by the rollers, andthrough the rollers, to give a controlled and uniform level oftreatment. The level of treatment was controlled by the concentration ofthe treatment chemicals in the treatment solution which was generally adissolved starch solution. The paper was captured below the two rollersand immediately dried on a drum drier set at about 100° C. The paper wasdried to about a 3-5% moisture level.

The size press formulations were prepared by dissolving starch for 45minutes at 95° C., cooling, holding the starch at 65° C. Generally thestarch pH was adjusted to 7.5. To the starch was added other additivesfor this treatment such as salt, sizing agents, and the glycol etherbased polymers used in this invention. Once the additives were in thestarch solution the solution pH was readjusted to a pH of 7.5. Then thestarch solution, still at 65° C. was used to treat the paper. For eachbase paper used the amount of solution picked up through the rollers wasdetermined and the additive levels set accordingly. After drying, eachsample was conditioned by aging at room temperature for seven days. Thesamples were also conditioned for at least 12 hours prior to beingtested under the conditions they would be tested.

Other samples used in the examples below were prepared on Hercules'pilot paper machine. The paper was made with conditions similar to thosedescribed above for Western Michigan University. Again the goal was tomake standard copy paper. On the Hercules paper machine the first driersection was followed by a size press and then another drier section andthen a set of calendering rolls. The treatments of the invention wereapplied to the paper at the size press. A puddle size press mode wasused. In the puddle mode, the liquid treatment solution was held alongthe rolls as a puddle through which the paper passed. The pilot machineprocess imitated the process of a large paper machine. As withlaboratory studies a solution of cooked (dissolved) starch was used asthe carrier for treatment chemicals.

Sizing Test

Descriptions of various sizing tests can be found in The Handbook ofPulping and Papermaking by Christopher J. Biermann Acedemic Press 1996,San Diego, ISBN 0-12-097362-6. Properties of Paper: An Introduction ed.William E. Scott and James C. Abbott Tappi Press 1995, Atlanta, ISBN0-89852-062-2. The Hercules Sizing Test (HST) was used for the currentwork. It is described by Tappi Method T530. For the test resultspresented in this disclosure a solution containing 1% napthalene greendye and 1% formic acid was used as the penetrant. The end point of thetest was set at 80% reflectance.

Ink-Jet Printing Conditions

Paper samples were printed with a Hewlett Packard HP6122 printer usingHP45 black ink cartridges. The settings for the printer were: plainpaper, normal print quality, color, no color enhancement. On each samplea solid black five inch by five inch square was printed and allowed todry before being stacked.

Image Analysis for Mottle and Strike-Through

Mottle and strike-through are both variations of uniformity, mottle ofblack print and strike-through of the white back side of paper that hasbeen printed. An image analysis method was used to quantify thevariations. Images were captured by a dual light scanner at a resolutionof 600 dpi in bit-map format. The images were then analyzed with amottle analysis software package from Verity IA 2004 MultifunctionVersion 1.4.1 designed by Roy R. Rosenberger. The software does astochastic analysis. Mottle values can be obtained for various targetsizes. A paper by Roy R. Rosenberger of Appleton, Wis. explains theanalysis. The paper “Stochastic Frequency Distribution Analysis asApplied to Mottle Measurement” can be obtained on the VerityIA web sitewww.verityia.com. For the results presented in this disclosure blackprinted samples were used and the luminance values of the printed areaswere evaluated on a grey scale. In the analysis, three values areobtained: 1) the standard deviation of the standard deviation ofluminance values of each target on a grey scale; 2) the mean of thestandard deviation of the luminance values; and 3) the standarddeviation of the means of the standard deviation of the luminancevalues. These values are multiplied together to obtain what is called aMottle Number.

For the examples presented in this disclosure, one target size isreported. First the 600 dpi images were taken. Then each image wasanalyzed as a collection of squares (a target size) of 16 dots by 16dots (a 0.67 mm by 0.67 mm square) across approximately a 55 mm by 55 mmarea. Across the image, groups of four squares were combined into alarger square. Each large square was a target of 1.4 mm by 1.4 mm. Thenumbers for the analysis of the mottle was determined for the collectionof 1.4 by 1.4 mm squares across the selected image area. The softwareprovided a mottle number for the 1.4×1.4 mm targets. In the analysis, ahigher value indicates more mottle. A lower value represents a moreuniform image and is desirable.

The same procedure was used for quantifying strike-through.

Measuring Optical Density

As noted above, optical density is a reflectance measurement. For thevalues of the current disclosure, an optical densitometer from GraphicsMicrosystems Inc. was used. The model was a Cosar 200. Black opticaldensities were measured and reported. Six readings were taken for eachsample and averaged. A higher optical density value represents lessreflectance and thus a darker looking print.

In all of the above tests, it is not so much the absolute values thatare of importance but rather the relative values versus control samplesthat were included in all tests. The control samples are described ineach example.

EXAMPLES Example 1 Demonstration of the Problem of Lowering InternalSizing Levels When No Glycol Based Polymer is Present

Using the pilot paper machine process described earlier and theconditions listed here three different paper samples were prepared withdifferent levels of internal sizing and only starch and sodium chlorideapplied at the size press. The sizing (liquid hold-out property) of thefinal paper was determined by the Hercules Sizing Test described above.The mottle and strike-through were determined on ink-jet printed blacksquares as described earlier.

The paper was made with 70:30 ratio of bleached craft hardwood andsoftwood as suitable for fine paper. 15% of a medium size precipitatedcalcium carbonate (Albacar 5970) was added based on the pulp solids.Likewise 0.75% cationic starch, 0.25% papermakers alum (Al2O3*14H20),0.015% of an anionic polyacrylamide retention aid, and three differentlevels of alkyl succinic anhydride (ASA) sizing agent were added on thesame basis. The ASA was added as a stable emulsion typical forpapermaking. At the size press, each sample was treated with a watersolution of 8% oxidized starch and 0.5% sodium chloride to give anaddition of 4% starch and 0.25% sodium chloride to the final dry paper.

The following table lists the results. Less ASA sizing agent resulted inless sizing and more mottle and strike-through when printed.

Sample ASA level HST (sec) Mottle Strike-Through 1. 0.036% 3 5.84 12.02. 0.046% 69 5.15 11.2 3. 0.060% 131 2.68 2.61 HST = Hercules Sizingtest

Example 2 Demonstration of the Problem of Increasing Surface SizingLevels with No Glycol Based Polymer.

The same conditions of Example 1 were used. At the size press, HerculesimPress® ST900 sizing agent (ST900) was added along with the starch.ST900 is an emulsion containing alkenyl ketene dimer as a sizing agent.The levels of addition on a dry basis of the dimer to the final paperwere 0 and 0.05%.

The results for sizing mottle and strike-through are listed in thefollowing table. Adding some surface sizing increased the sizing but themottle and strike-through were worse.

Sample dimer level HST (sec) Mottle Strike-Through 1. 0 3 5.84 12.0 2.0.050 189 27.0 18.3

Example 3 Addition of Premixed Polyethyleneglycol and Magnesium Chloride

Samples were prepared in the laboratory using a bench top size press andpre-made base sheet by the process described above. The base sheetcontained 1.25#/ton of a solid AKD sizing agent applied as an emulsion(Hercules' Hercon® 70 sizing emulsion). It also contained 10% Albacar HOPCC filler. The compositions of the paper treatments applied at the sizepress were based on a 9% solution, in water, of a low viscosity oxidizedstarch (D-15F from Grain Processing Corporation). The pick-up of thebase sheet of the starch solution was 54.0%. Therefore, the final papercontained approximately (54×0.09)/(100+(54×0.09)×100% or 4.64% starch.Addition levels of additives were based on this pick-up. To eachformulation enough NaCl was added to give a final paper content of0.25%. Enough reactive sizing agent, non-reactive sizing agent, glycolether polymer and MgCl₂ was added to give the desired levels of additionas listed in the following table. The reactive sizing agent used was astable emulsion of liquid dimer based on a saturated alkyl fatty acid(AKD). The unreactive sizing agent was a styrene acidic emulsion type(SAE) consisting of a poly(styrene/butyl acrylate) emulsion (Hercules'Chromaset 800 product). The glycol ether polymer was a polyethyleneglycol (PEG) of 1000 g/mole average molecular weight. Both the MgCl2 andPEG were pre-mixed with the dimer emulsion before being added to thestarch solution. The results for the final paper sizing, mottle,strike-through and optical density (OD) are also listed in the table.

Values listed for materials are percent of final paper weight. The HSTvalues are in seconds.

Dimer SAE PEG MgCl₂ HST Mottle St. Thr. OD A. 0.035 0.018 0 0 496 16.28.29 1.23 B. 0.045 0.023 0 0 515 18.0 2.78 1.32 C. 0.035 0.018 0.007 0449 10.2 2.24 1.37 D 0.045 0.023 0.009 0 477 2.1 0.60 1.42 E 0.035 0.0180 0.053 477 22.9 4.58 1.29 F. 0.045 0.023 0 0.068 513 11.0 2.04 1.45 G0.035 0.018 0.007 0.053 378 23.0 4.31 1.32 H 0.045 0.023 0.009 0.068 4310.7 0.42 1.47

The addition of PEG improved mottle, strike-through, and opticaldensity. The sizing was not compromized. Addition of MgCl₂ loweredsizing a little but also improved mottle, strike-through, and opticaldensity. Addition of both materials had a significant effect on sizingand at the lower level did not improve mottle. However, at the higherlevel mottle, strike-through, and optical density improved. The benefitsof MgCl₂ were known from previous work but the benefit obtained from PEGwas surprising. Surprisingly, the benefits of divalent metals salts andPEG were additive.

Example 4 Addition of Polypropylene Glycol

Using the pilot paper machine described earlier with wet-end conditionsconsisting of 75/25 hard wood/soft wood, 16% PCC, 0.07% dimer from anAKD emulsion, alum, cationic starch, and anionic polyacrylamideretention aid the effect of the additions of starch with NaCl, liquiddimer emulsion and polypropyleneglycol (PPG) were tested. The level ofstarch, NaCl, and dimer in the final paper samples were constant andwere 4%, 0.25%, and 0.035%, respectively.

The wet-end conditions were as follows:

-   -   The cationic starch used was Stalok 400 from Staley    -   The level of cationic starch was 0.75% of the final paper weight    -   AKD stands for Alkyl Ketene Dimer Sizing Agent. The commercial        product used was Hercules Hercon 70 sizing agent.    -   The alum level was 0.25% based on final paper weight    -   The level of anionic polyacrylamide retention aid was 0.015%        based on final paper weight    -   The temperature was 50° C.    -   The pH was 7.0    -   The basis weight of the paper formed was 75 grams per square        meter of paper

The size press conditions were as follows:

-   -   The starch used was an oxidized corn starch called D15F from        Grain Processing Corporation    -   The starch was cooked for 40 minutes at 95° C.    -   The starch solution concentration was 7.5%    -   The temperature of the size press solution was 65° C. The liquid        dimer sizing agent used was Hercules imPress ST900 sizing agent.

The level of PPG added is listed below in the table of results. The PPGhad an average molecular weight of 700 g/mole.

Sample PPG (%) HST (sec) Mottle Str-Thr  A. 0 268 16.4 51.6 B 0.01% 22914.6 37.4 C 0.02% 70 12.0 17.2

PPG was only slightly effective at lowering mottle. It was effective atreducing strike-through. However, at 0.01% and 0.02% in the paper itreduced the level of sizing. Example 5 Addition of polyethyleneglycoldiglycidyl ether and polypropylene glycol diglycidyl ether.

The pilot paper machine described above was used to test theeffectiveness of PEG and PPG with glycidyl ether (epoxide) end groups.The conditions were the same as in example 4, except the wet-end sizingwas alkyl succinic anhydride (ASA). The pH was 7.8 instead of 7.0

Paper was made with two levels of ASA, 0.036 and 0.041%. A 75/25 hardwood/soft wood mixture was used with 16% PCC filler, 0.75% cationicstarch, 0.5% paper makers alum, and 0.015% anionic retention aid. Thepaper was then treated on the paper machine at the size press.

Polyethyleneglycol diglycidyl ether (PEGDGE) with an average molecularweight of about 350 g/mole and polypropylene glycol diglycidyl ether(PPGDGE) with an average molecular weight of about 400 g/mole were mixedwith an oxidized starch and a liquid ketene dimer sizing agent made froman unsaturated alkyl fatty acid. The sizing agent was added as anemulsion to the starch solution. The glycol ether polymers were alsoadded to the starch solution. The level of starch added to the paper was4%. As is typical in fine paper manufacturing 0.25% NaCl was added tothe paper by also adding NaCl to the size press starch solution. Thelevels of dimer and glycol ether polymers in the final papers are notedbelow.

(the levels of materials are listed in dry percent of the final paperweight.)

I. 0.036% ASA in the Base Sheet

Sample Dimer Polymer HST Mottle Str. Th. OD A 0.05 none 181 8.38 3.181.27 B 0.065 none 195 13.6 3.35 1.32 C 0.05 0.01 PEGDGE 169 9.79 3.221.34 D 0.065 0.01 PEGDGE 181 2.80 0.735 1.41 E 0.05 0.02 PEGDGE 154 2.161.05 1.38 F 0.065 0.02 PEGDGE 192 2.24 0.814 1.39 G 0.05 0.01 PPGDGE 1621.16 0.921 1.43 H 0.05 0.02 PPGDGE 126 1.51 0.722 1.43

II. 0.041% ASA in the Base Sheet

Sample Dimer Polymer HST Mottle Str. Th. OD A 0.04 none 174 2.39 1.361.41 B 0.055 none 185 1.13 0.57 1.43 C 0.04 0.0075 PEGDGE 158 1.17 0.621.42 D 0.055 0.0075 PEGDGE 180 0.905 0.53 1.43 E 0.04  0.015 PEGDGE 1561.02 0.83 1.41 F 0.055  0.015 PEGDGE 148 0.88 0.54 1.42 G 0.04 0.0075PPGDGE 164 0.82 0.71 1.43 H 0.055 0.0075 PPGDGE 201 0.94 0.65 1.43

Both PEGDGE and PPGDGE reduced mottle and strike-through. The benefitdepends on the amount of mottle and strike-through of the paper withoutthem. The samples with more internal ASA had less mottle andstrike-through and therefore the amount of improvement was less. PPGDGEwas more effective than PEGDGE. However, when 0.02% PPGDGE was used thesizing was reduced. At lower levels, it may also have a negative effecton sizing when a low level of sizing agent is used. As an added benefit,both epoxides enhanced optical density. PPGDGE was again more effectivethan PEGDGE.

Example 6 Addition of Alternative Functionalized Glycol Ether Polymers

Using the same conditions as Example 3, except for use of an 8% ratherthan a 9% starch solution, poly(ethylene glycol) bis (carboxymethyl)ether (PEGBCME) was evaluated. The polymer was obtained from Alrich andhad an average molecular weight of 600. The results are displayed in thefollowing table.

Values listed for materials are percent of final paper weight. The HSTvalues are in seconds.

Dimer PEGBCME Mottle St. Thr. A. 0.04 0 15.0 10.5 B. 0.04 0.0075 4.7514.3 C. 0.04 0.015 1.13 5.25 PEGBCME reduced mottle and strike-through.

Example 7 Use of a pre-mixture

Using the same conditions as Example 3, except for use of a 10% starchsolution instead of a 9% starch solution, a pre-mixture of sizing agentand glycol ether polymer was evaluated.

ImPress® ST900 sizing emulsion of Hercules was used as the sizing agenton its own and in pre-mixtures with PPG. The PPG was predispersed inwater, 10% PPG and 90% water, with a sonicator. The PPG dispersion wasmixed with the dimer emulsion. The ratio of dimer to PPG in thepre-mixtures was 10 to 1 and 5 to 1. The results of the evaluation aresummarized in the following table.

Dimer PPG HST Mottle St.Thr. A. 0.035 0 384 28.9 8.56 C. 0.035 0.0035392 29.4 5.56 E. 0.035 0.007 349 16.6 4.83

PPG was premixed with a dimer emulsion and the mottle and strike-throughperformance of the treated paper was improved. With the lowest level ofPPG, 0.0035%, there was little or no improvement of mottle butstrikethrough improved. At a higher level the mottle and strikethroughperformance of the paper improved. As noted in a previous example, theaddition of too much PPG will reduce the level of sizing.

1. An uncoated cellulosic paper having a front and a back surface,having been treated on at least one surface with: a) at least one sizingagent present in an amount of between 0.01 to 0.3% based on dry weightof paper; b) starch present in an amount of between 1 to 8% based on dryweight of paper c) a glycol ether based polymer present in an amountless than 0.025% based on dry weight of paper and optionally, a divalentmetal salt.
 2. The cellulosic paper of claim 1 wherein the glycol etherbased polymers primary backbone is selected from polyethylene glycol, orpolypropylene glycol.
 3. The cellulosic paper of claim 1 wherein theglycol ether based polymers have glycidyether functional groups.
 4. Thecellulosic paper of claim 1 wherein the glycol ether based polymersprimary backbone is selected from polyethyleneglycol diglycidyl ether orpolypropylene glycol diglycidyl ether.
 5. The cellulosic paper of claim1 wherein the sizing agent is selected from alkyl succinic anhydride,ketene dimers, or alkenyl ketene dimers.
 6. An aqueous composition forsurface treating paper through a size press, which composition contains:a) Sizing agent in an amount of 0.03-1.0%, b) starch present in anamount of 1.5-12% c) a glycol ether based polymer present in an amountof less than 0.25% of the composition.
 7. The composition of claim 6wherein the glycol ether polymers primary backbone is eitherpolyethylene glycol or polypropylene glycol.
 8. The composition of claim6 wherein the glycol ether polymers primary backbone Is selected frompolyethyleneglycol diglycidyl ether or polypropylene glycol diglycidylether.
 9. The composition of claim 6 wherein the glycol ether basedpolymers have glycidyl ether based functional groups.
 10. Thecomposition of claim 6 wherein the sizing agent is selected from alkylsuccinic anhydride, ketene dimers, or alkenyl ketene dimers.
 11. Processfor improving ink-jet printing properties of paper which comprisestreating paper with a composition of claim
 6. 12. Process of claim 11wherein the glycol ether based polymer is selected from polyethyleneglycol, polypropylene glycol, polyethyleneglycol diglycidyl ether, orpolypropylene glycol diglycidyl ether.
 13. Process of claim 11 whereinthe glycol ether based polymers have glycidyl ether functionality. 14.The process of claim 12 wherein the sizing agent is a reactive sizingagent.
 15. Process of claim 11 wherein the sizing agent is selected fromalkyl succinic anhydride, ketene dimers, or alkenyl ketene dimers. 16.The cellulosic paper of claim 1 wherein the sizing agent is acombination of a reactive dimer sizing agent and a polymeric latexsizing agent.
 17. The process of claim 12 wherein the sizing agent is acombination of a reactive dimer sizing agent and a polymeric latexsizing agent.
 18. Aqueous composition containing a glycol ether basedpolymer and an emulsified sizing agent where the glycol ether basedpolymer is present in an amount of 3-50% based on amount of sizingagent.
 19. The cellulosic paper of claim 1 wherein the starch is presentin an amount of between 2 to 7%, and the glycol ether based polymer ispresent in an amount less than 0.02%.